Materials Literature
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The mechanism of stoichiometric enantioselective alkene epoxidations by the D4- and D2-symmetric homochiral trans-dioxoruthenium(VI) porphyrins, [RuVI(D4-Por*)O2] (1) and [RuVI(D2-Por*)O2] (2a), in the presence of pyrazole (Hpz) was studied by UV/Vis spectrophotometry and analysis of the organic products. The enantios…
Polycrystalline boron carbon nitride (BCN) films are synthesized by plasma-assisted chemical vapor deposition. The dielectric constant is estimated from the accumulation region of capacitance–voltage characteristics of Cu/BCN/p-Si samples. It is found that the dielectric constant of the BCN film is reduced by annealin…
Well-aligned boron nanowire arrays were grown vertically on silicon substrates over areas up to several tens of square centimeters using radio-frequency magnetron sputtering of highly pure boron. During growth and self-assembly of boron nanowire arrays, no template or catalyst was needed. The morphology, structure, an…
Edle Partikel: Durch einfaches Mischen bei Raumtemperatur von Ag-, Au-, Pd- oder Pt-Salzen mit reduzierten Polyoxometallaten, die als Photokatalysatoren und Stabilisatoren dienen, ließen sich ultrafeine Metall-Nanopartikel erhalten (siehe Reaktionszyklus).
The dielectric properties of (1−x)Pb(Mg1/3Nb2/3)O3−(x)PbTiO3 (PMN–PT) crystals have been investigated over a temperature range of 4 to 450 K at various frequencies. At low temperatures, an unusual frequency dependent plateau region in the absorption was observed between 75 and 175 K. At both higher and lower temperatu…
The substrate electronic effects on the selectivity in the catalytic epoxidation of para-substituted cis stilbenes 2a-i were investigated by using (R,R)-[N,N'-bis(3,5-di-tBu-salicylidene)-1,2-cyclohexanediamine]manganese(III) chloride 1 in benzene as the catalyst with iodosobenzene as the terminal oxidant. A Hammett s…
The anomalous enhancement in dielectric (ε>6000) and piezoelectric constant (d33>600 pC/N) in the tetragonal side (x=35%) of morphotropic phase boundary (MPB) has been observed in polycrystalline (1−x)Pg(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT). On the other hand, x-ray peak position shifts under electric field (E…
A series of chiral double hydrophilic block copolymers (DHBCs) was synthesized and employed as additives in the crystallization of calcium tartrate tetrahydrate (CaT). We found that appropriate polymers can slow down the formation of the thermodynamically most stable racemic crystals as well as the formation of one of…
Epitaxial CrO2(100) island films have been grown on TiO2(100) substrates by a chemical-vapor deposition technique. Well-controlled surface and interface properties of the CrO2(100) films were confirmed by scanning tunneling microscopy and transmission electron microscopy, respectively. Spin- and angle-resolved photoem…
Entscheidend ist die Mikrostruktur: Der erstmalige Einsatz von zwiebelförmigem Kohlenstoff in der heterogenen Katalyse belegt die Leistungsfähigkeit solcher Materialien in Anwendungen wie der hier untersuchten oxidativen Dehydrierung von Ethylbenzol zu Styrol (siehe schematische Darstellung).
Fein abstimmbare Eigenschaften: Eine Familie dreidimensionaler Gerüst-Indiumchalkogenide wird vorgestellt, die nicht auf Clustern basiert. Die Zusammensetzung des Gerüsts ist hoch flexibel und kontrollierbar. Solch eine Vielfalt bei der Zusammensetzung ermöglicht die Abstimmung struktureller, elektronischer und optisc…
Dendritische Multichromophore auf der Grundlage eines starren Polyphenylen-Gerüstes enthalten bis zu drei verschiedene Rylen-Chromophore: im fokalen Punkt, im Gerüst und an der Peripherie des Dendrimers. Dadurch wird ein Energiegradient zwischen der Peripherie und dem Dendrimerkern erzeugt, und intramolekularer Transf…
Eng verwandt mit der (P)2.614-Helix von γ-Peptiden: Das Harnstoff-Heptamer 1 nimmt in Lösung eine stabile, 2.5-helicale Sekundärstruktur ein, die durch eine Ganghöhe von etwa 5.1 Å sowie 12- und 14-gliedrige Wasserstoffbrückenringe charakterisiert ist. N,N′-verknüpfte Oligoharnstoffe gehören somit zu der wachsenden Fa…
Square-shaped hydrogen-bonded polar nanotubes are formed when the C4-symmetrical all-S cyclotetraurea bearing side chains of alanine self-assembles in the solid state (see picture). The four urea fragments in the macrocyle present an all-trans planar conformation with an unidirectional alignment of all the carbonyl gr…
Chiral smectic A liquid crystal materials of the de Vries type (with molecules tilted relative to the layer normal) exhibit analog field-induced (electroclinic) optic axis rotation accompanied by an increase in birefringence. We identify two such de Vries smectic A* materials and use them to develop and test models fo…
Poly(propylene imine) dendrimers that are modified with long alkyl chains self-assemble to form well-defined aggregates. The geometry and surface chemistry of the dendrimer assemblies can be varied through the addition of surfactants. These dendrimer/surfactant aggregates can be tuned to template the formation of the…
Contrast agent for magnetic resonance imaging: The exchangeable amide protons in the Yb3+ complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide (see crystal structure) act as efficient antennae for transfer of saturated spins to bulk water. Saturation of all eight protons in a 5 mM solution of this complex…
Durch chemische Funktionalisierung einwandiger Kohlenstoffnanoröhren werden die Voraussetzungen für mögliche Anwendungen solcher Nanostrukturen geschaffen. Derivatisierte Röhren zeichnen sich im Unterschied zum Rohmaterial u. a. durch eine gute Löslichkeit aus und sind so einer umfangreichen Charakterisierung und Folg…
We have investigated the change of atomic and electronic structures of fluorinated single-walled carbon nanotubes (SWCNTs) using x-ray photoemission spectroscopy (XPS), electrical resistivity measurements, and transmission electron microscopy (TEM). The fluorine content increases with increasing reaction temperature u…
Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds (FeII(pz)[Ag(CN)2]2).pz (pz = pyrazine), (FeII(4,4'-bipy)2[Ag(CN)2]2) (4,4'-bipy = 4,4'-bipyridine), and (FeII(bpe)2[Ag(CN)2]2) (bpe = bispyridylethylene), respectively. The sing…